Rewrite `sysconfig.get_config_vars` data generation to receive clearly-defined inputs

Feature or enhancement

Proposal:

Right now, some of the data is calculated during import, then we use that to calculate more data when building the sysconfig.get_config_vars cache. It would be good to transform all of this into a clearly defined algorithm, where we the data is generated based on a set of inputs, making it easier to generate data when cross-compiling, and allowing us to generate data for a specific environment (eg. source builds, vs installed build). This would have helped mitigate issues such as GH-127429, GH-128055, and GH-126789.

Additionally, this also gives us the opportunity to split the data into two sets: the minimum needed to evaluate the install scheme paths, and the non-critical additional data we expose in sysconfig.get_config_vars. This would help with the bootstrapping issue in python -m sysconfig --generate-posix-vars.

https://github.com/python/cpython/blob/f802c8bf872ab882d3056675acc79c950fe5b93c/Lib/sysconfig/__main__.py#L206-L221

Has this already been discussed elsewhere?

No response given

Links to previous discussion of this feature:

No response

Lib/sysconfig/main.pyから始め、特にリンク先の206–221行とpython -m sysconfig --generate-posix-varsのフローを確認してください。インポート時およびキャッシュ生成時に構成データがどのように計算されるかを追跡してください。データ生成アルゴリズムの入力が明確に定義され、クロスコンパイルやインストール済みビルドなどの異なる環境をサポートし、インストールスキームのデータと追加で公開される変数が分離されていれば完了です。